Well, if Natsu joins Zeref in a fanfiction, it might start with Natsu being forced into it somehow. Maybe Zeref has some sort of leverage over Natsu, like threatening his friends. Natsu would then have to figure out how to work with Zeref while still holding onto his own values. Their relationship could be very strained at first. But as time goes on, they could start to understand each other better and even develop a sort of begrudging respect for one another.
In a Natsu joins Zeref fanfiction, one possibility is that Natsu could initially be conflicted. He has always seen Zeref as an enemy, but perhaps there's a common goal they discover. For example, they might find out about a greater evil that threatens the entire magical world. Natsu's fiery nature could be used in a new way when combined with Zeref's dark magic. This could lead to a very different power dynamic compared to what we see in the original Fairy Tail story.
A Natsu joins Zeref fanfiction could be really interesting. Natsu is all about life and friendship, while Zeref is associated with death and destruction. Their union could be a way to explore the balance between these two extremes. It could also lead to some great character development for both of them. Natsu might learn more about the dark side of magic and Zeref could be reminded of the good in the world through Natsu. And there could be a lot of action as they face off against foes who are both afraid and intrigued by their new alliance.
If Natsu and Zeref join Fairy Tail in fanfiction, it would change the dynamic of the guild completely. The other members would have mixed reactions. Some might be distrustful of Zeref due to his past actions. However, as time passes, they could see the good in him. Natsu and Zeref together could attract a lot of attention from outside forces. Enemies might target Fairy Tail more because of their combined power. But also, they could inspire the guild to become even stronger, with everyone striving to keep up with their new powerful comrades.
He might lose his friends at Fairy Tail. Since Fairy Tail is all about friendship and light, joining a dark guild would put him at odds with his former comrades.
Well, it could be chaos. Zeref's dark powers would likely disrupt the harmony of Fairy Tail at first. His presence might cause a lot of suspicion and fear among the guild members.
In this fanfiction scenario, one possible thing that could happen is that Natsu's determination to defeat Zeref might be put to the ultimate test. Natsu has always been a fighter with a strong will, and facing Zeref, he would have to dig deep. Zeref, on the other hand, being extremely powerful, might initially have the upper hand. But Natsu could tap into some hidden power, perhaps related to his dragon slayer magic in a new and unexpected way. Maybe he would get some kind of emotional boost from his friends in Fairy Tail who are watching, which gives him the edge he needs to turn the battle around.
Well, perhaps Zeref kidnaps Natsu because he sees Natsu as a key to some grand plan. Maybe he wants to use Natsu's power for his own dark purposes. For example, Zeref might think Natsu's unique magic can help him break some sort of ancient curse or gain access to a powerful magic source.
Well, one possible plot could be that Zeref kidnaps Natsu in an attempt to use his power for some dark purpose. Maybe he wants to turn Natsu into a weapon against Fairy Tail. Zeref might believe that Natsu's unique dragon - slayer magic can be harnessed in a way that no one else's can.
Naruto's moral compass would be greatly affected. Zeref has a much darker view of the world compared to Naruto. So, Naruto might start to see things in a more cynical way. He could view his old enemies as mere pawns in a bigger game. This would lead to a lot of internal conflict as he tries to reconcile his old self with this new Zeref - influenced mindset. His friends would try to pull him back from the brink, but it would be a difficult battle.
Most of the Fairy Tail members would not take it well. Happy, Natsu's closest friend, would be extremely confused and sad. He'd follow Natsu around, trying to get him to come back to the guild. Makarov, the guild master, would see it as a huge threat to the guild's safety. He might send some of the stronger members to keep an eye on Natsu and Zeref. And the younger members like Wendy would look up to Natsu so much that they'd be very disappointed and scared for him, thinking that he's making a big mistake by joining Zeref.
Maybe some unexpected allies could emerge. For instance, other dark mages who oppose Zeref's actions for their own reasons. They might see Natsu as a valuable asset or simply dislike Zeref's overbearing ways. Another potential ally could be a powerful spirit that Natsu has befriended in the past. Spirits often have unique powers that could be useful in the fight against Zeref.
It could be another dark mage who sees the potential in baby Natsu and wants to use him for evil purposes. This mage might view Zeref as an obstacle in getting to Natsu.